One lone wolf turned the tide for this isolated group, report Scandinavian researchers. Past studies have suggested that dwindling populations could be resuscitated by new blood. But this is the first time scientists have spotted this boost in the wild, said Carles Vilà, a co-author of the study.

"Natural immigration may be extremely important for the recovery of small populations that are isolated," said Vilà, a conservation geneticist at Uppsala University, Sweden.

The study was published November 21 online in Proceedings of the Royal Society of London, Series B.

The Wolf Mystery

Wolves started vanishing from Scandinavia during the last century, and were thought to be extinct by the 1960s.

In the 1980s, a small group of roaming wolves reappeared. Hans Ellegren of Uppsala University, also a co-author of the study, said controversy swirled around the new pack's origins. Some thought the wolves had re-emerged from hiding. Others spread rumors of illegally-released animals or dogs run wild.

Ellegren and his colleagues tracked the pack's beginnings by following unique DNA markers, called microsatellites. By tracing these markers back through history, they determined that a single pair of wolves had started the first pack.

To uncover the homeland of the original pair, the researchers compared the genetic make-up of the founder wolves against likely possibilities. They pulled DNA samples from wolf teeth from the early 20th century, found tucked away in museum collections. Samples from modern-day packs in Russia and Finland also served time in the lab.

The team determined that a pair of wolves made the unlikely 620-mile (1,000-kilometer) journey from Finland to start a new Scandinavian pack. With no outside visitors, however, the emerging pack was mired in its own genes. Genetic snapshots caught the same genes recycling through the isolated Scandinavian population.